Melting temperature distribution and fractionation in the lower mantle

Eiji Ohtani

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64 Citations (Scopus)

Abstract

The melting curve of perovskite MgSiO3 and the liquidus and solidus curves of the lower mantle were estimated from thermodynamic data and the results of experiments on phase changes and melting in silicates. The initial slope of the melting curve of perovskite MgSiO3 was obtained as dTm/dP{reversed tilde equals}77 K GPa-1 at 23 GPa. The melting curve of perovskite was expressed by the Kraut-Kennedy equation as Tm(K)=917( 1+29.6ΔV V0), where Tm≳2900 K and P≳23 GPa; and by the Simon equation, P(GPa)-23=21.2[ (Tm(K) 2900)1.75-1]. The liquidus curve of the lower mantle was estimated as Tliq {reversed tilde equals} 0.9 Tm (perovskite) and this gives the liquidus temperature Tliq=7000 ±500 K at the mantle-core boundary. The solidus curve of the lower mantle was also estimated by extrapolating the solidus curve of dry peridotite using the slope of the solidus curve of magnesiowüstite at high pressures. The solidus temperature is ∼ 5000 K at the base of the lower mantle. If the temperature distribution of the mantle was 1.5 times higher than that given by the present geotherm in the early stage of the Earth's history, partial melting would have proceeded into the deep interior of the lower mantle. Estimation of the density of melts in the MgOFeOSiO2 system for lower mantle conditions indicates that the initial melt formed by partial fusion of the lower mantle would be denser than the residual solid because of high concentration of iron into the melt. Thus, the melt generated in the lower mantle would tend to move downward toward the mantle-core boundary. This downward transportation of the melt in the lower mantle might have affected the chemistry of the lower mantle, such as in the D″ layer, and the distribution of the radioactive elements between mantle and core.

Original languageEnglish
Pages (from-to)12-25
Number of pages14
JournalPhysics of the Earth and Planetary Interiors
Volume33
Issue number1
DOIs
Publication statusPublished - 1983 Aug

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Geophysics
  • Physics and Astronomy (miscellaneous)
  • Space and Planetary Science

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